Imaging lens

ABSTRACT

An imaging lens including, in order from an object side towards an image surface side, a diaphragm, a first lens which is a meniscus lens having a positive power whose convex surface faces the object side, and a second lens which is a lens having a positive power whose convex surface faces the image surface side, wherein conditions expressed by each of following expressions (1)-(6) are to be satisfied; 1.25≧L/fl≧0.8, 1≧f 1 /f 2 ≧0.2, 1.8≧f 1 /fl≧1, 0.5&gt;d 2 /d 1 ≧0.2, 0.35≧d 1 /fl≧0.1, and 0.27≧d 3 /fl≧0.1 (where, L: entire length of the lens system, fl: focal distance of the entire lens system, f 1 : focal distance of the first lens, f 2 : focal distance of the second lens, d 1 : center thickness of the first lens, d 2 : space between the first lens and the second lens on the optical axis, and d 3 : center thickness of the second lens).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging lens. In particular, thepresent invention relates to an imaging system of a two-lens structurethat is capable of reducing size and weight, enhancing opticalperformance, and improving productivity. The imaging lens is used for animage-taking device that forms an image of an object, such as scenery ora person, on an image-taking surface of a solid image pickup device suchas a CCD, CMOS, etc. The solid image pickup device is mounted on aportable computer, a television phone, a portable phone, a digitalcamera, and the like.

2. Description of the Related Art

Recently, there has been an increasing demand for cameras that utilize asolid image pickup device, such as a CCD, CMOS, or the like, which ismounted on a portable phone, a portable computer, and a televisionphone, for example. It is demanded that a camera such as this is smalland light because the camera is required to be mounted on a limitedinstallation space.

Therefore, it is also necessary for the imaging lens used for suchcameras to be similarly small and light. Conventionally, a single-lensstructure lens system using a single lens is used as such imaging lens.

Such a single-lens structure lens system can sufficiently handle beingapplied to a solid image pickup device called CIF that has a resolutionof about 110 thousand pixels. However, in recent years, the use of asolid image pickup device called VGA that has a high resolution of about300 thousand pixels is being examined. There is a problem in that theconventional single-lens structure lens system cannot sufficiently exertthe resolution performance of such high-resolution solid image pickupdevices.

Therefore, conventionally, various two-lens structure lens systems andthree-lens structure lens systems having an optical performance that issuperior to that of the single-lens structure lens system have beenproposed.

In this case, in the three-lens structure lens system, each aberrationleading to the deterioration of the optical performance can beeffectively corrected, thereby allowing an extremely high opticalperformance to be obtained. However, since the three-lens structure lenssystem has a large number of parts, it is difficult to reduce the sizeand weight. Since each component part requires high accuracy, themanufacturing costs increase, as well.

On the other hand, although the two-lens structure lens system cannotachieve an optical performance that is as high as that of the three-lensstructure lens system, a higher optical performance than that of thesingle-lens structure lens system can be acquired. It can be said thatthe two-lens structure lens system is suitable for a small,high-resolution solid image pickup device.

As such a two-lens structure lens system, conventionally, numerous lenssystems called a retro-focus-type in which a negative lens and apositive lens are combined have been proposed. It is possible to reducecosts of such retro-focus-type lens systems through a reduction of thenumber of parts. However, from this configuration, it is practicallyimpossible to reduce the size and weight to about the size and weight ofthe single-lens structure lens system since the back focus distanceincreases.

As another two-lens structure lens system, there is a lens system calleda telephoto-type in which a positive lens and a negative lens arecombined. However, such telephoto-type lens systems had been developedfor silver-salt photography, and therefore, the back focus distance ofthe telephoto-type lens system is too short. The telephoto-type lenssystem also has problems regarding telecentricity. It is difficult toapply the telephoto-type lens system as is to the imaging lens for solidimage pickup devices.

Furthermore, conventionally, in the two-lens structure lens system orthe three-lens structure lens system, a configuration in which adiaphragm is disposed between two lenses that are mutually adjacent inthe optical axis direction is mainstream (for example, refer to PatentLiteratures 1 and 2).

[Patent Literature 1] Japanese Patent Unexamined Publication 2004-163850

[Patent Literature 2] Japanese Patent Unexamined Publication 2004-170460

There is an increasing demand for further improvement of the opticalperformance, in addition to the reduction in size and weight, of thesetypes of imaging lens. However, in a configuration in which thediaphragm is disposed between the two lenses, as in the imaging lensdescribed in Patent Literatures 1 and 2, it is difficult to achieve boththe reduction in size and weight and further improvement in the opticalperformance. Furthermore, it is difficult to accommodate the sensorcharacteristics (incident angle to the sensor).

SUMMARY OF THE INVENTION

Therefore, the present invention has been designed in view of theaforementioned problems. The object of the present invention is toprovide an imaging lens that can sufficiently meet the demands for thereduction in size and weight and further improvement in the opticalperformance, and improve productivity.

In the present specifications, productivity means not only theproductivity for mass-producing imaging lens (for example, moldability,cost, and the like when imaging lens are mass-produced by injectionmolding), but also easiness of processing, manufacture, etc. ofequipment (for example, easiness of processing and the like of a moldused for injection molding), which is used for manufacturing the imaginglens.

In order to achieve the aforementioned object, the imaging lensaccording to a first aspect of the present invention is an imaging lensused for forming an image of an object on an image-taking surface of asolid image pickup device, which comprises, in order from an object sidetowards an image surface side: a diaphragm, a first lens which is ameniscus lens having a positive power whose convex surface faces theobject side, and a second lens which is a lens having a positive powerwhose convex surface faces the image surface side, wherein conditionsexpressed by each of following expressions (1)-(6) are to be satisfied;1.25≧L/fl≧0.8  (1)1≧f ₁ /f ₂≧0.2  (2)1.8≧f ₁ /fl≧1  (3)0.5>d ₂ /d ₁≧0.2  (4)0.35≧d ₁ /fl≧0.1  (5)0.27≧d ₃ /fl≧0.1  (6)where,

L: entire length of the lens system

fl: focal distance of the entire lens system

f₁: focal distance of the first lens

f₂: focal distance of the second lens

d₁: center thickness of the first lens

d₂: space between the first lens and the second lens on the optical axis

d₃: center thickness of the second lens.

In the first aspect of the present invention, the diaphragm is disposedat a position closest to the object side. Thereby, it becomes possibleto secure high telecentricity, and the incident angle of a light ray tothe sensor of the solid image pickup device can be made more obtuse.

In the present invention, the diaphragm being disposed at a positionclosest to the object side does not interfere with the diaphragm beingdisposed in the same position on the optical axis direction as a pointon the optical axis on the object side face (convex face) of the firstlens, or the object side face of the first lens in the vicinity of theoptical axis being positioned closer to the object side than thediaphragm through the diaphragm. Even in this case, the diaphragm isdisposed at a position closer to the object side than the entire firstlens, as a physical disposition. Therefore this does not go against thedescriptions in the claims.

In addition, in the first aspect of the present invention, the firstlens is a meniscus lens having a positive power whose convex surfacefaces the object side, the second lens is a lens having a positivepower, and the power of each lens is regulated to satisfy each conditionexpressed by the expressions (1)-(6). With this, it is possible toimprove productivity, while reducing size and weight.

An imaging lens according to a second aspect is the imaging lensaccording to the first aspect, wherein, further, the second lens is ameniscus lens.

In the second aspect of the present invention, further, it is possibleto improve the optical performance of the periphery without placing aload on the shapes of the first lens and the second lens and moreeffectively use the light ray irradiated on the periphery of the solidimage pickup device.

An imaging lens according to a third aspect is the imaging lensaccording to the first aspect, wherein, further, the object side surfaceof the second lens is convex towards the object side in the vicinity ofthe optical axis and is formed into an aspheric surface having aninflection point.

In the third aspect of the present invention, further, it is possible tofurther reduce the load placed on the shape of each lens and furtherimprove the optical performance of the periphery. In addition, it ispossible to more effectively use the light ray irradiated on theperiphery of the solid image pickup device.

An imaging lens according to a fourth aspect is the imaging lensaccording to the third aspect, wherein, further, an outer end section ofan effective diameter of the object side face of the second lens ispositioned closer to the object side than a point on the optical axis onthe object side surface of the second lens.

In the fourth aspect of the present invention, further, it is possibleto further improve the optical performance of the periphery. Inaddition, there are advantages not only when handling the lenses, butalso during assembly when the lenses are mounted on a barrel and madeinto a unit.

An imaging lens according to a fifth aspect is the imaging lensaccording to any one of aspects 1 to 4, wherein, further, a conditionexpressed by a following expression (7) is to be satisfied;10≧f ₂ /fl≧1.5  (7).

In the fifth aspect of the present invention, further, the expression(7) is satisfied. Thereby, productivity can be further improved, whileappropriately securing the necessary back focus distance.

An imaging lens according to a sixth aspect is the imaging lensaccording to aspect 5, wherein, further, the diaphragm satisfies acondition expressed by a following expression (8);0.2≧S  (8)where,

S: distance between the diaphragm and the optical surface closest to theobject side on the optical axis.

In the sixth aspect of the invention, further, the expression (8) issatisfied. Thereby, telecentricity can be more effectively secured andthe size and weight can be further reduced.

An imaging lens according to a seventh aspect is the imaging lensaccording to aspect 6, wherein, further, a condition expressed by afollowing expression (9) is to be satisfied;0.8≧Bfl/fl≧0.4  (9)where,

Bfl: back focus distance (distance from the last lens surface to theimage-taking surface on the optical axis (air reduced length)).

In the seventh aspect of the invention, further, the expression (9) issatisfied. Thereby, the size and weight can be more effectively reduced,and productivity and manageability when assembling can be furtherimproved.

An imaging lens according to an eighth aspect is the imaging lensaccording to aspect 7, wherein, further, a condition expressed by afollowing expression (10) is to be satisfied;2.5≧Bfl≧0.8  (10).

In the eighth aspect of the invention, further, the expression (10) issatisfied. Thereby, the size and weight can be more effectively reduced,and productivity and manageability when assembling can be furtherimproved.

With the imaging lens according to the first aspect of the presentinvention, it is possible to achieve an imaging lens that has reducedsize and weight, superior optical performance, and excellentproductivity.

Further, in addition to the effects of the imaging lens according to thefirst aspect, the imaging lens according to the second aspect canachieve a small imaging lens that has a better improved opticalperformance, while maintaining excellent productivity, and can moreeffectively use the light ray irradiated on the periphery of the solidimage pickup device.

Further, in addition to the effects of the imaging lens according to thefirst aspect, the imaging lens according to the third aspect can achievea small imaging lens that has more superior optical performance, whilemaintaining excellent productivity, and can more effectively use thelight ray irradiated on the periphery of the solid image pickup device.

Further, in addition to the effects of the imaging lens according to thethird aspect, the imaging lens according to the fourth aspect canachieve an imaging lens that has more superior optical performance,while maintaining excellent productivity, and can more effectively usethe light ray irradiated on the periphery of the solid image pickupdevice.

Further, in addition to the effects of the imaging lens according to anyone of aspects 1 to 4, the imaging lens according to the fifth aspectcan achieve an imaging lens that has more excellent productivity.

Further, in addition to the effects of the imaging lens according to anyone of aspects 1 to 5, the imaging lens according to the sixth aspectcan achieve an imaging lens that more effectively secures telecentricityand has more reduced size and weight.

Further, in addition to the effects of the imaging lens according to anyone of aspects 1 to 6, the imaging lens according to the seventh aspectcan achieve an imaging lens that has more reduced size and weight andmore excellent productivity.

Further, in addition to the effects of the imaging lens according to anyone of aspects 1 to 7, the imaging lens according to the eighth aspectcan achieve an imaging lens that is suitable for further reduction insize and weight and further improvement in productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for showing an embodiment of the imaginglens according to the present invention;

FIG. 2 is a schematic diagram for showing FIRST EXAMPLE of the imaginglens according to the present invention;

FIG. 3 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 2;

FIG. 4 is a schematic diagram for showing SECOND EXAMPLE of the imaginglens according to the present invention;

FIG. 5 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 4;

FIG. 6 is a schematic diagram for showing THIRD EXAMPLE of the imaginglens according to the present invention;

FIG. 7 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 6;

FIG. 8 is a schematic diagram for showing FOURTH EXAMPLE of the imaginglens according to the present invention;

FIG. 9 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 8;

FIG. 10 is a schematic diagram for showing FIFTH EXAMPLE of the imaginglens according to the present invention;

FIG. 11 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 10;

FIG. 12 is a schematic diagram for showing SIXTH EXAMPLE of the imaginglens according to the present invention;

FIG. 13 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 12;

FIG. 14 is a schematic diagram for showing SEVENTH EXAMPLE of theimaging lens according to the present invention;

FIG. 15 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 14;

FIG. 16 is a schematic diagram for showing EIGHTH EXAMPLE of the imaginglens according to the present invention;

FIG. 17 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 16;

FIG. 18 is a schematic diagram for showing NINTH EXAMPLE of the imaginglens according to the present invention;

FIG. 19 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 18;

FIG. 20 is a schematic diagram for showing TENTH EXAMPLE of the imaginglens according to the present invention;

FIG. 21 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 20;

FIG. 22 is a schematic diagram for showing ELEVENTH EXAMPLE of theimaging lens according to the present invention;

FIG. 23 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 22;

FIG. 24 is a schematic diagram for showing TWELFTH EXAMPLE of theimaging lens according to the present invention;

FIG. 25 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 24;

FIG. 26 is a schematic diagram for showing THIRTEENTH EXAMPLE of theimaging lens according to the present invention;

FIG. 27 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 26;

FIG. 28 is a schematic diagram for showing FOURTEENTH EXAMPLE of theimaging lens according to the present invention;

FIG. 29 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 28;

FIG. 30 is a schematic diagram for showing FIFTEENTH EXAMPLE of theimaging lens according to the present invention; and

FIG. 31 shows graphs for describing the spherical aberration,astigmatism, and distortion of the imaging lens shown in FIG. 30.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the imaging lens according to the present inventionwill be described hereinafter by referring to FIG. 1.

As shown in FIG. 1, an imaging lens 1 of the embodiment comprises, inorder from the object side towards the image surface side, a diaphragm2, a resin-type first lens 3 which is a meniscus lens having a positivepower with its convex surface facing the object side, and a resin-typesecond lens 4 which is a lens having a positive power with its convexsurface facing the image surface side.

Herein, each of the lens surfaces on the object side and the imagesurface side of the first lens 3 and the second lens 4 is respectivelyreferred to as a first face and a second face.

On the second face side of the second lens 4, there are disposed variousfilters 6 such as a cover glass, an IR cut filter, and a lowpass filter,and an image-taking surface 7 which is a light-receiving surface of animage sensor element such as a CCD or a CMOS, respectively. The variousfilters 6 may be omitted as required.

The closer the position of the diaphragm 2 is to the image surface side,the closer the position of the exit pupil is to the image surface side.As a result, it becomes difficult to secure telecentricity. An off-axislight emitted from the imaging lens 1 is irradiated at an angle to thesensor of the solid image pickup device.

On the other hand, in the embodiment, the exit pupil can be positionedat a position far from the sensor face (image-taking surface) of thesolid image pickup device, by the diaphragm 2 being disposed at aposition closest to the object side.

Therefore, in the embodiment, high telecentricity can be secured and theincident angle of the light ray in relation to the sensor of the solidimage pickup device can be made more obtuse.

In addition, in the embodiment, the diaphragm 2 is disposed on theobject side of the first lens 3, and the first lens 3 has ameniscus-shape of which its convex surface faces the object side.Thereby, the second face of the first lens 3 can be effectively used.

Further, in the embodiment, the shape of the second face of the secondlens 4 is convex towards the image surface side. Thereby, a highertelecentricity can be secured, and the incident angle to the sensor ofthe solid image pickup device can be more effectively controlled. Stillfurther, the shape of the second face of the second lens 4 is morepreferably an aspherical surface in which the curvature becomes largerthe farther away from the optical axis 8 it is. With this, a highertelecentricity can be secured and the incident angle to the sensor ofthe solid image pickup device can be more effectively controlled.

Further, in the embodiment, the imaging lens 1 is to satisfy eachcondition expressed by the following expressions (1)-(6).1.25≧L/fl≧0.8  (1)1≧f ₁ /f ₂≧0.2  (2)1.8≧f ₁ /fl≧1  (3)0.5>d ₂ /d ₁≧0.2  (4)0.35≧d ₁ /fl≧0.1  (5)0.27≧d ₃ /fl≧0.1  (6)where, L in the expression (1) is the entire length of the lens systemi.e., the optical distance between the surface physically closest to theobject side and the image-taking surface. More specifically, when thefirst surface of the first lens 3 in the vicinity of the optical axis 8is positioned closer to the image surface side than the diaphragm 2, thedistance from the diaphragm 2 to the image-taking surface is L. At thesame time, as described above, when the first surface of the first lens3 in the vicinity of the optical axis 8 is positioned closer to theobject side than the diaphragm 2 through the diaphragm 2, the distancefrom the first surface of the first lens 3, rather than the diaphragm 2,to the image-taking surface becomes L. In addition, when the diaphragm 2is disposed at the same position in the optical axis 8 direction as thepoint on the optical axis 8 of the first surface of the first lens 3,the distance from the diaphragm 2 and the first surface of the firstlens 3 to the image-taking surface becomes L. fl in the expressions (1),(3), (5), and (6) is the focal distance of the entire lens system. f₁ inthe expressions (2) and (3) is the focal distance of the first lens 3.f₂ in the expressions (2) and (4) is the focal distance of the secondlens 4. d₁ in the expressions (4) and (5) is the center thickness of thefirst lens 3. d₂ in the expression (4) is the space between the firstlens 3 and the second lens 4 on the optical axis 8. d₃ in the expression(6) is the center thickness of the second lens 4.

When the value of the L/fl exceeds the value (1.25) shown in theexpression (1), the entire optical system becomes too large and goesagainst the demand for reduction in size and weight. At the same time,when the L/fl becomes below the value (0.8) shown in the expression (1),the entire optical system becomes small. Thus, productivity isdeteriorated and it becomes difficult to maintain the opticalperformance. In addition, it becomes difficult to secure the necessaryback focus distance.

Therefore, by further setting the value of L/fl to satisfy theexpression (1) in the embodiment, the size and weight of the imaginglens system can be sufficiently reduced, while maintaining the requiredback focus distance, and an excellent optical performance can bemaintained.

It is more preferable for the relation between L and fl to satisfy anexpression 1.2≧L/fl≧1.05.

Further, when the value of f₁/f₂ exceeds the value (1) shown in theexpression (2), the power of the first lens 2 becomes so strong that theproductivity is deteriorated. In addition, the back focus distancebecomes too long, making it difficult to reduce the size of the entireoptical system. At the same time, when the value of f₁/f₂ becomes belowthe value (0.2), the productivity of the first lens 3 is deterioratedand it becomes difficult to secure the necessary back focus distance.

Therefore, by further setting the f₁/f₂ to satisfy the expression (2) inthe embodiment, productivity can be further improved and the size andweight of the entire optical system can be sufficiently reduced, whilemore effectively securing the necessary back focus distance.

It is more preferable for the relation between f₁ and f₂ to satisfy anexpression 0.9≧f₁/f₂≧0.55.

Further, when the value of f₁/fl exceeds the value (1.8) shown in theexpression (3), the back focus distance becomes too long, thereby makingit difficult to reduce the size and weight. At the same time, when thevalue of f₁/fl becomes below the value (1) shown in the expression (3),the productivity of the first lens is deteriorated.

Therefore, by further setting the value of f₁/fl to satisfy theexpression (3) in the embodiment, the size and weight can be furtherreduced and productivity can be improved

It is more preferable for the relation between f₁ and fl to satisfy anexpression 1.6≧f₁/fl≧1.

Still further, when the value of d₂/d₁ becomes the value (0.5) shown inthe expression (4) or larger, the power of the first lens 3 and thesecond lens 4 is required to be increased, thereby making it difficultto manufacture each lens 3 and 4. In addition, the height of the lightray passing through the image surface side face of the second lens 4 ishigh. Therefore, the power of the aspherical surface increases andmanufacturing becomes more difficult. At the same time, when the valueof d₂/d₁ is below the value (0.2) shown in the expression (4), thecenter thickness of the first lens 3 becomes relatively too thick. Thus,it becomes difficult to secure the back focus distance and insert adiaphragm that effectively limits the amount of light.

Therefore, by further setting the value of d₂/d₁ to satisfy theexpression (4) in the embodiment, productivity can be further improved,the necessary back focus distance can be more appropriately secured, andmore excellent optical performance can be maintained.

It is more preferable for the relation between d₂ and d₁ to satisfy anexpression 0.5>d₂/d₁≧0.3.

Still further, when the value of d₁/fl exceeds the value (0.35) shown inthe expression (5), the entire length of the optical system becomes toolong, thereby making it difficult to reduce the size and weight. At thesame time, when the value of d₁/fl is below the value (0.1) shown in theexpression (5), it becomes difficult to manufacture the first lens 3.

Therefore, by further setting the value of d₁/fl to satisfy theexpression (5) in the embodiment, the size and weight can be furtherreduced and productivity can be improved.

It is more preferable for the relation between d₁ and fl to satisfy anexpression 0.25≧d₁/fl≧0.15.

Still further, when the value of d₃/fl exceeds the value (0.27) shown inthe expression (6), the entire length of the optical system becomes toolong, thereby making it difficult to reduce the size and weight. At thesame time, when the value of d₃/fl is below the value (0.1) shown in theexpression (6), it becomes difficult to manufacture the second lens 4.

Therefore, by further setting the value of d₃/fl to satisfy theexpression (6) in the embodiment, the size and weight of the entireoptical system can be further reduced and productivity can be improved.

It is more preferable for the relation between d₃ and fl to satisfy anexpression 0.25≧d₃/fl≧0.15.

In addition to the above-described structures, the second lens 4 ispreferably a meniscus lens.

In this case, the optical performance of the periphery can be improvedwithout placing a load on the shapes of the first lens 3 and the secondlens 4 and the light ray irradiated on the periphery of the solid imagepickup device can be more effectively used.

Furthermore, the first surface of the second lens 4 in the vicinity ofthe optical axis 8 preferably has a convex surface facing the objectside and is formed into an aspherical surface having an inflectionpoint.

Herein, the inflection point of the first surface of the second lens 4is a point on a cross-section of the second lens 4 that includes theoptical axis 8, in which a tangent contacting a curved line (a curvedline on the cross-section) on the first surface of the second lens 4changes the symbol of its angle.

Therefore, as described above, when the center section of the firstsurface of the second lens 4 has a convex surface facing the objectside, the surface shape of the peripheral section surrounding the centersection of the first surface changes to a concave surface facing theobject side with the inflection point as the boundary.

As a result, the optical performance of the periphery can be improvedwithout placing a load on the shapes of the first lens 3 and the secondlens 4 and the light rays respectively passing through the lenses 3 and4 can be more effectively used.

The first face of the second lens 4 can have a surface shape in which aplurality of inflection points appears toward the periphery from theoptical axis 8. In this case, the various aberrations can be morefavorably corrected.

Further, in addition to the above-described structures, the outer endsection of the effective diameter of the object side face of the secondlens is preferably positioned closer to the object side than the pointon the optical axis on the object side surface of the second lens 4.

As a result, the optical performance of the periphery can be furtherimproved. In addition, there are advantages not only when handling thelenses, but also during assembly when the lenses are mounted on a barreland made into a unit.

Further, in addition to the above-described structures, it is moredesirable to satisfy the following expression (7).10≧f ₂ /fl≧1.5  (7)

Herein, when the value of f₂/fl exceeds the value (10) shown in theexpression (7), the productivity of the first lens 3 deteriorates and itbecomes difficult to maintain the necessary back focus distance. At thesame time, when the value of f₂/fl becomes below the value (1.5) shownin the expression (7), the power of the second lens 4 becomes toostrong, thereby deteriorating the productivity.

Therefore, by further setting the value of f₂/fl to satisfy theexpression (7) in the embodiment, the productivity can be furtherimproved while further appropriately maintaining the necessary backfocus distance.

It is more preferable for the relation between f₂ and fl to satisfy anexpression 6≧f₂/fl≧1.5.

Further, in addition to the above-described structures, it is moredesirable if the diaphragm 2 satisfies the following expression (8).

S in the expression (8) is the distance between the diaphragm 2 and theoptical surface closest to the object side on the optical axis 8. Inother words, S is the distance between the diaphragm 2 and the firstface of the first lens 3 on the optical axis 8. In addition, S is aphysical distance. The diaphragm 2 can be positioned closer to eitherthe object side or the image surface side than the point on the opticalaxis 8 on the first face of the first lens 3.0.2≧S  (8)

When S=0, the position of the diaphragm in the optical axis 8 directionis the same position as the point on the optical axis 8 on the firstface of the first lens 3.

As a result, telecentricity can be further effectively maintained andthe size and weight can be further reduced.

It is more preferable that S is 0.15≧S.

Further, in addition to the above-described structures, it is moredesirable to satisfy the following expression (9).

However, Bfl in the expression (9) is the back focus distance or, inother words, the distance from the last lens surface (second face of thesecond lens 4) to the image-taking surface 7 on the optical axis 8 (airreduced length).0.8≧Bfl/fl≧0.4  (9)

As a result, the size and weight can be more effectively reduced, andproductivity and manageability when assembling can be further improved.

It is more preferable for the relation between Bfl and fl to satisfy anexpression 0.7≧Bfl/fl≧0.5.

Further, in addition to the above-described structures, it is moredesirable to satisfy the following expression (10).2.5≧Bfl≧0.8  (10)

As a result, the size and weight can be more effectively reduced, andproductivity and manageability when assembling can be further improved.

It is more preferable that Bfl is 2.0≧Bfl≧1.0.

Further, in addition to the above-described structures, it is moredesirable that fl satisfies 5≧fl≧1 (more preferably 3.5≧fl≧1.5).

As a result, a configuration that is more suitable for a lens used in acamera module that is mounted on a portable terminal and the like can beachieved.

Moreover, examples of a resin material used for molding the first lens 3and the second lens 4 may be materials of various compositions withtransparency, such as acryl, polycarbonate, amorphous polyolefin resin,etc. However, from the perspective of further improving themanufacturing efficiency and further reducing the manufacturing costs,it is preferable that the resin materials of both lenses 3 and 4 areunified and are the same resin material.

EXAMPLES

Next, EXAMPLES of the present invention will be described by referringto FIG. 2 or FIG. 31.

In the EXAMPLES, F no denotes F number and r denotes the curvatureradius of the optical surface (the center radius curvature in the caseof a lens). Further, d denotes a distance to the next optical surface,nd denotes the index of refraction when the d line (yellow) isirradiated, and vd denotes the Abbe number of each optical system alsowhen the d line is irradiated.

k, A, B, C, and D denote each coefficient in a following expression(11). Specifically, the shape of the aspherical surface of the lens isexpressed by the following expression provided that the direction of theoptical axis 8 is taken as the Z axis, the direction orthogonal to theoptical axis 8 as the X axis, the traveling direction of light ispositive, k is the constant of cone, A, B, C, and D are the asphericalcoefficients, and r is the curvature radius.

$\begin{matrix}{{Z(X)} = {{r^{- 1}{X^{2}/\left\lbrack {1 + \left\{ {1 - {\left( {k + 1} \right)r^{- 2}X^{2}}} \right\}^{1/2}} \right\rbrack}} + {AX}^{4} + {BX}^{6} + {CX}^{8} + {DX}^{10}}} & (11)\end{matrix}$

In the following EXAMPLES, reference code E used for a numerical valuedenoting the constant of cone and the aspherical coefficient indicatesthat the numerical value following E is an exponent having 10 as thebase and that the numerical value before E is multiplied by thenumerical value denoted by the exponent having 10 as the base. Forexample, −1.48E−1 denotes −1.48×10⁻¹.

First Example

FIG. 2 shows a FIRST EXAMPLE of the present invention. In the FIRSTEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the FIRST EXAMPLE was set under the followingcondition.

Lens Data L = 4.34 mm, fl = 3.85 mm, f₁ = 5.18 mm, f₂ = 8.42 mm, d₁ =0.9 mm, d₂ = 0.44 mm, d₃ = 0.8 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.270 0.90 1.531 56.0 3 (Second Face of First Lens) 1.778 0.44 4 (FirstFace of Second Lens) −57.143 0.80 1.531 56.0 5 (Second Face of SecondLens) −4.167 0.00 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.48E−1 2.52E−2 −1.56E−3 −2.11E−1 5.05E−1 3 −1.90 7.03E−2 8.47E−29.66E−2 −1.61E−2 4 −2.43E+5 −2.31E−1 2.82E−1 −3.96E−1 0 5 −3.89E−1−3.44E−2 −7.73E−2 8.63E−2 −4.31E−2

Under such conditions, L/fl=1.13 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.62 was achieved, thereby satisfying theexpression (2). f₁/fl=1.35 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.49 was achieved, thereby satisfying theexpression (4). d₁/fl=0.23 was achieved, thereby satisfying theexpression (5). d₃/fl=0.21 was achieved, thereby satisfying theexpression (6). f₂/fl=2.19 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.57 was achieved, thereby satisfying the expression (9).Bfl=2.2 mm was achieved, thereby satisfying the expression (10).

FIG. 3 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the FIRST EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Second Example

FIG. 4 shows a SECOND EXAMPLE of the present invention. In the SECONDEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the SECOND EXAMPLE was set under the followingcondition.

Lens Data L = 2.19 mm, fl = 1.94 mm, f₁ = 2.7 mm, f₂ = 3.91 mm, d₁ =0.48 mm, d₂ = 0.2 mm, d₃ = 0.4 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)0.645 0.48 1.531 56.0 3 (Second Face of First Lens) 0.870 0.20 4 (FirstFace of Second Lens) −50.000 0.40 1.531 56.0 5 (Second Face of SecondLens) −2.000 0.00 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.48E−1 1.80E−1 −4.24E−1 −2.97E+1 2.78E+2 3 −2.20 5.19E−1 2.431.23E+1 −8.24 4 −2.43E+5 −1.80 8.68 −5.13E+1 0 5 −1.47 −2.57E−1 −2.361.10E+1 −2.27E+1

Under such conditions, L/fl=1.13 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.69 was achieved, thereby satisfying theexpression (2). f₁/fl=1.39 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.42 was achieved, thereby satisfying theexpression (4). d₁/fl=0.25 was achieved, thereby satisfying theexpression (5). d₃/fl=0.21 was achieved, thereby satisfying theexpression (6). f₂/fl=2.02 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.57 was achieved, thereby satisfying the expression (9).Bfl=1.11 mm was achieved, thereby satisfying the expression (10).

FIG. 5 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the SECOND EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Third Example

FIG. 6 shows a THIRD EXAMPLE of the present invention. In the THIRDEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the THIRD EXAMPLE was set under the followingcondition.

Lens Data L = 2.09 mm, fl = 1.86 mm, f₁ = 2.37 mm, f₂ = 4.55 mm, d₁ =0.5 mm, d₂ = 0.18 mm, d₃ = 0.4 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)0.625 0.50 1.525 56.0 3 (Second Face of First Lens) 0.909 0.18 4 (FirstFace of Second Lens) −20.000 0.40 1.525 56.0 5 (Second Face of SecondLens) −2.151 0.00 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.48E−1 1.81E−1 −2.67E−1 −2.74E+1 3.22E+2 3 −1.72 5.93E−1 2.971.23E+1 −8.24 4 −2.43E+5 −1.86 7.95 −5.31E+1 0 5 7.93E−1 −2.85E−1 −2.431.05E+1 −2.38E+1

Under such conditions, L/fl=1.12 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.52 was achieved, thereby satisfying theexpression (2). f₁/fl=1.27 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.36 was achieved, thereby satisfying theexpression (4). d₁/fl=0.27 was achieved, thereby satisfying theexpression (5). d₃/fl=0.22 was achieved, thereby satisfying theexpression (6). f₂/fl=2.45 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.54 was achieved, thereby satisfying the expression (9).Bfl=1.01 mm was achieved, thereby satisfying the expression (10).

FIG. 7 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the THIRD EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Fourth Example

FIG. 8 shows a FOURTH EXAMPLE of the present invention. In the FOURTHEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the FOURTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.32 mm, fl = 2.06 mm, f₁ = 2.74 mm, f₂ = 4.63 mm, d₁ =0.55 mm, d₂ = 0.16 mm, d₃ = 0.45 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)0.699 0.55 1.531 56.0 3 (Second Face of First Lens) 0.980 0.16 4 (FirstFace of Second Lens) −33.333 0.45 1.531 56.0 5 (Second Face of SecondLens) −2.299 0.00 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.48E−1 1.36E−1 −1.66E−1 −1.41E+1 1.36E+2 3 −1.72 4.45E−1 1.85 6.34−3.49 4 −2.43E+5 −1.40 4.93 −2.72E+1 0 5 7.93E−1 −2.14E−1 −1.51 5.39−1.01E+1

Under such conditions, L/fl=1.13 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.59 was achieved, thereby satisfying theexpression (2). f₁/fl=1.33 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.29 was achieved, thereby satisfying theexpression (4). d₁/fl=0.27 was achieved, thereby satisfying theexpression (5). d₃/fl=0.22 was achieved, thereby satisfying theexpression (6). f₂/fl=2.25 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.56 was achieved, thereby satisfying the expression (9).Bfl=1.16 mm was achieved, thereby satisfying the expression (10).

FIG. 9 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the FOURTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Fifth Example

FIG. 10 shows a FIFTH EXAMPLE of the present invention. In the FIFTHEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the FIFTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.31 mm, fl = 2.05 mm, f₁ = 2.72 mm, f₂ = 4.61 mm, d₁ =0.55 mm, d₂ = 0.15 mm, d₃ = 0.45 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)0.698 0.55 1.531 56.0 3 (Second Face of First Lens) 0.978 0.15 4 (FirstFace of Second Lens) −31.429 0.45 1.531 56.0 5 (Second Face of SecondLens) −2.292 0.00 6 (First Face of Cover Glass) 0.000 0.30 1.518 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.48E−1 1.43E−1 −1.26E−1 −1.38E+1 1.38E+2 3 −1.73 4.44E−1 1.86 6.34−3.49 4 −2.43E+5 −1.41 4.79 −2.81E+1 0 5 −8.26E−1 −1.94E−1 −1.49 5.34−1.02E+1

Under such conditions, L/fl=1.13 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.59 was achieved, thereby satisfying theexpression (2). f₁/fl=1.33 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.27 was achieved, thereby satisfying theexpression (4). d₁/fl=0.27 was achieved, thereby satisfying theexpression (5). d₃/fl=0.22 was achieved, thereby satisfying theexpression (6). f₂/fl=2.25 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.57 was achieved, thereby satisfying the expression (9).Bfl=1.16 mm was achieved, thereby satisfying the expression (10).

FIG. 11 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the FIFTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Sixth Example

FIG. 12 shows a SIXTH EXAMPLE of the present invention. In the SIXTHEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the SIXTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.26 mm, fl = 1.99 mm, f₁ = 2.59 mm, f₂ = 4.68 mm, d₁ =0.55 mm, d₂ = 0.15 mm, d₃ = 0.45 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)0.690 0.55 1.531 56.0 3 (Second Face of First Lens) 1.000 0.15 4 (FirstFace of Second Lens) −33.333 0.45 1.531 56.0 5 (Second Face of SecondLens) −2.326 0.00 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.48E−1 1.47E−1 −1.49E−1 −1.40E+1 1.38E+2 3 −1.71 4.46E−1 1.86 6.34−3.49 4 −2.43E+5 −1.44 4.59 −3.00E+1 0 5 −5.22E−1 −1.97E−1 −1.50 5.30−1.00E+1

Under such conditions, L/fl=1.14 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.55 was achieved, thereby satisfying theexpression (2). f₁/fl=1.30 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.27 was achieved, thereby satisfying theexpression (4). d₁/fl=0.28 was achieved, thereby satisfying theexpression (5). d₃/fl=0.23 was achieved, thereby satisfying theexpression (6). f₂/fl=2.35 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.56 was achieved, thereby satisfying the expression (9).Bfl=1.11 mm was achieved, thereby satisfying the expression (10).

FIG. 13 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the SIXTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Seventh Example

FIG. 14 shows a SEVENTH EXAMPLE of the present invention. In the SEVENTHEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the SEVENTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.22 mm, fl = 2.02 mm, fl = 2.8 mm, f₂ = 4.56 mm, d₁ = 0.5mm, d₂ = 0.13 mm, d₃ = 0.3 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)0.697 0.50 1.531 56.0 3 (Second Face of First Lens) 0.980 0.13 4 (FirstFace of Second Lens) −33.333 0.30 1.531 56.0 5 (Second Face of SecondLens) −2.273 0.00 6 0.000   (Image Surface) Face Number k A B C D 2−1.48E−1 8.29E−1 −2.16E+1 −6.43E+1 2.94E+3 3 7.25 −4.40E−1 −1.75E+1 6.34−3.49 4 −2.43E+5 −2.07 1.55E+1 −2.28E+2 0 5 9.31 −7.29E−1 4.99 −3.47E+14.31E+1

Under such conditions, L/fl=1.10 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.61 was achieved, thereby satisfying theexpression (2). f₁/fl=1.39 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.26 was achieved, thereby satisfying theexpression (4). d₁/fl=0.25 was achieved, thereby satisfying theexpression (5). d₃/fl=0.15 was achieved, thereby satisfying theexpression (6). f₂/fl=2.26 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.64 was achieved, thereby satisfying the expression (9).Bfl=1.29 mm was achieved, thereby satisfying the expression (10).

FIG. 15 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the SEVENTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Eighth Example

FIG. 16 shows an EIGHTH EXAMPLE of the present invention. In the EIGHTHEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the EIGHTH EXAMPLE was set under the followingcondition.

Lens Data L = 3.41 mm, fl = 2.9 mm, f₁ = 4.36 mm, f₂ = 5.6 mm, d₁ = 0.65mm, d₂ = 0.32 mm, d₃ = 0.75 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.087 0.65 1.531 56.0 3 (Second Face of First Lens) 1.622 0.32 4 (FirstFace of Second Lens) 7.906 0.75 1.531 56.0 5 (Second Face of SecondLens) −4.613 0.30 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.83 8.88E−2 5.02E−1 −9.42E−1 1.01 3 −3.19E−1 1.64E−2 4.04E−1 −1.563.03 4 −7.93 −1.92E−1 2.08E−1 −2.01 6.02 5 −4.97E−2 −2.50E−2 −1.14E−2−5.94E−2 7.13E−2

Under such conditions, L/fl=1.18 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.78 was achieved, thereby satisfying theexpression (2). f₁/fl=1.50 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.49 was achieved, thereby satisfying theexpression (4). d₁/fl=0.22 was achieved, thereby satisfying theexpression (5). d₃/fl=0.26 was achieved, thereby satisfying theexpression (6). f₂/fl=1-93 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.58 was achieved, thereby satisfying the expression (9).Bfl=1.69 mm was achieved, thereby satisfying the expression (10).

FIG. 17 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the EIGHTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Ninth Example

FIG. 18 shows a NINTH EXAMPLE of the present invention. In the NINTHEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the NINTH EXAMPLE was set under the followingcondition.

Lens Data L = 3.70 mm, fl = 3.39 mm, f₁ = 4.36 mm, f₂ = 10.44 mm, d₁ =0.65 mm, d₂ = 0.32 mm, d₃ = 0.75 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.087 0.65 1.531 56.0 3 (Second Face of First Lens) 1.622 0.32 4 (FirstFace of Second Lens) 7.906 0.75 1.531 56.0 5 (Second Face of SecondLens) −17.929 0.00 6 (First Face of Cover Glass) 0.000 0.00 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −7.77E−1 −1.52E−3 1.52E−1 4.39E−2 3.82E−2 3 −3.42 7.39E−2 −1.69E−1−5.66E−1 1.18 4 −1.36E+1 −1.60E−1 −2.72E−1 −1.53 6.99 5 1.01E−1 −4.35E−2−2.01E−2 8.25E−2 −1.98E−1

Under such conditions, L/fl=1.09 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.42 was achieved, thereby satisfying theexpression (2). f₁/fl=1.29 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.49 was achieved, thereby satisfying theexpression (4). d₁/fl=0.19 was achieved, thereby satisfying theexpression (5). d₃/fl=0.22 was achieved, thereby satisfying theexpression (6). f₂/fl=3.08 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.58 was achieved, thereby satisfying the expression (9).Bfl=1.98 mm was achieved, thereby satisfying the expression (10).

FIG. 19 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the NINTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Tenth Example

FIG. 20 shows a TENTH EXAMPLE of the present invention. In the TENTHEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of TENTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.33 mm, fl = 2.15 mm, f₁ = 2.83 mm, f₂ = 6.42 mm, d₁ =0.4 mm, d₂ = 0.17 mm, d₃ = 0.4 mm, F no = 4.0 Face Number r d nd νd  (Object Point) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.425 0.40 1.531 56.0 3 (Second Face of First Lens) 0.950 0.10 4 (FirstFace of Second Lens) 0.195 0.40 1.531 56.0 5 (Second Face of SecondLens) −0.100 0.30 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.97 −2.97E−1 2.21E+1 −3.05E+2 1.51E+3 3 −1.03E+1 −4.44E−1 2.01−1.47E+2 3.51E+2 4 0.00 −1.54 −2.67 −3.03E+2 4.35E+3 5 0.00 −3.28E−1−1.31 6.96 −4.50E+1

Under such conditions, L/fl=1.08 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.44 was achieved, thereby satisfying theexpression (2). f₁/fl=1.32 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.43 was achieved, thereby satisfying theexpression (4). d₁/fl=0.19 was achieved, thereby satisfying theexpression (5). d₃/fl=0.19 was achieved, thereby satisfying theexpression (6). f₂/fl=2.99 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.63 was achieved, thereby satisfying the expression (9).Bfl=1.355 mm was achieved, thereby satisfying the expression (10).

FIG. 21 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the TENTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Eleventh Example

FIG. 22 shows an ELEVENTH EXAMPLE of the present invention. In theELEVENTH EXAMPLE, like the imaging lens with the structure of FIG. 1, adiaphragm 2 is disposed on the object side of the first face of thefirst lens 3 and a cover glass is disposed between the second face ofthe second lens 4 and the image-taking surface 7, as a filter 6. Thediaphragm 2 is disposed at the same position on the optical axis 8 asthe point on the optical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the ELEVENTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.21 mm, fl = 2.06 mm, f₁ = 2.71 mm, f₂ = 6.09 mm, d₁ =0.4 mm, d₂ = 0.15 mm, d₃ = 0.35 mm, F no = 4.0 Face Number r d nd νd  (ObjectPoint) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.425 0.40 1.531 56.0 3 (Second Face of First Lens) 0.985 0.15 4 (FirstFace of Second Lens) 0.225 0.35 1.531 56.0 5 (Second Face of SecondLens) −0.085 0.30 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −3.26 −4.59E−2 3.25E+1 −4.90E+2 2.64E+3 3 −4.38 −1.55 1.35E+1−2.67E+2 5.62E+2 4 0.00 −2.65 2.91E+1 −1.10E+3 1.35E+4 5 0.00 −6.51E−14.86E−1 −6.60E−1 −5.10E+1

Under such conditions, L/fl=1.07 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.44 was achieved, thereby satisfying theexpression (2). f₁/fl=1.32 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.38 was achieved, thereby satisfying theexpression (4). d₁/fl=0.19 was achieved, thereby satisfying theexpression (5). d₃/fl=0.17 was achieved, thereby satisfying theexpression (6). f₂/fl=2.96 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.63 was achieved, thereby satisfying the expression (9).Bfl=1.305 mm was achieved, thereby satisfying the expression (10).

FIG. 23 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the ELEVENTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Twelfth Example

FIG. 24 shows a TWELFTH EXAMPLE of the present invention. In the TWELFTHEXAMPLE, like the imaging lens with the structure of FIG. 1, a diaphragm2 is disposed on the object side of the first face of the first lens 3and a cover glass is disposed between the second face of the second lens4 and the image-taking surface 7, as a filter 6. The diaphragm 2 isdisposed at the same position on the optical axis 8 as the point on theoptical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the TWELFTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.23 mm, fl = 2.05 mm, f₁ = 2.4 mm, f₂ = 8.4 mm, d₁ =0.4213 mm, d₂ = 0.2015 mm, d₃ = 0.3272 mm, F no = 4.0 Face Number r d ndνd   (ObjectPoint) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.215 0.42 1.531 56.0 3 (Second Face of First Lens) 0.394 0.20 4 (FirstFace of Second Lens) 0.015 0.32 1.531 56.0 5 (Second Face of SecondLens) −0.020 0.30 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.51 −7.61E−1 2.04E+1 −2.64E+2 9.09E+2 3 2.24E+1 −2.30 −1.92−1.10E+2 1.54E+2 4 0.00 −3.40 2.11E+1 −8.31E+2 9.36E+3 5 0.00 −1.03  1.95 −1.41E+1 1.44E+1

Under such conditions, L/fl=1.09 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.29 was achieved, thereby satisfying theexpression (2). f₁/fl=1.17 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.48 was achieved, thereby satisfying theexpression (4). d₁/fl=0.21 was achieved, thereby satisfying theexpression (5). d₃/fl=0.16 was achieved, thereby satisfying theexpression (6). f₂/fl=4.10 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.62 was achieved, thereby satisfying the expression (9).Bfl=1.278 mm was achieved, thereby satisfying the expression (10).

FIG. 25 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the TWELFTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Thirteenth Example

FIG. 26 shows a THIRTEENTH EXAMPLE of the present invention. In theTHIRTEENTH EXAMPLE, like the imaging lens with the structure of FIG. 1,a diaphragm 2 is disposed on the object side of the first face of thefirst lens 3 and a cover glass is disposed between the second face ofthe second lens 4 and the image-taking surface 7, as a filter 6. Thediaphragm 2 is disposed at the same position on the optical axis 8 asthe point on the optical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the THIRTEENTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.17 mm, fl = 1.91 mm, f₁ = 2.23 mm, f₂ = 8.82 mm, d₁ =0.42 mm, d₂ = 0.2 mm, d₃ = 0.4 mm, F no = 4.0 Face Number r d nd νd  (ObjectPoint) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.230 0.42 1.531 56.0 3 (Second Face of First Lens) 0.468 0.20 4 (FirstFace of Second Lens) 0.100 0.40 1.531 56.0 5 (Second Face of SecondLens) −0.115 0.30 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −2.06 −9.89E−1 4.78E+1 −8.61E+2 5.42E+3 3 2.83E+1 −2.01   3.37−1.39E+2 2.91E+2 4 0.00 −1.79 −1.20 −2.76E+2 3.79E+3 5 0.00 −3.04E−1−2.07   1.22E+1 −4.80E+1

Under such conditions, L/fl=1.14 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.25 was achieved, thereby satisfying theexpression (2). f₁/fl=1.17 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.48 was achieved, thereby satisfying theexpression (4). d₁/fl=0.22 was achieved, thereby satisfying theexpression (5). d₃/fl=0.21 was achieved, thereby satisfying theexpression (6). f₂/fl=4.62 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.60 was achieved, thereby satisfying the expression (9).Bfl=1.15 mm was achieved, thereby satisfying the expression (10).

FIG. 27 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the THIRTEENTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Fourteenth Example

FIG. 28 shows a FOURTEENTH EXAMPLE of the present invention. In theFOURTEENTH EXAMPLE, like the imaging lens with the structure of FIG. 1,a diaphragm 2 is disposed on the object side of the first face of thefirst lens 3 and a cover glass is disposed between the second face ofthe second lens 4 and the image-taking surface 7, as a filter 6. Thediaphragm 2 is disposed at the same position on the optical axis 8 asthe point on the optical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the FOURTEENTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.28 mm, fl = 2.03 mm, f₁ = 2.33 mm, f₂ = 10.05 mm, d₁ =0.42 mm, d₂ = 0.2 mm, d₃ = 0.4 mm, F no = 4.0 Face Number r d nd νd  (ObjectPoint) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.200 0.42 1.531 56.0 3 (Second Face of First Lens) 0.475 0.20 4 (FirstFace of Second Lens) 0.080 0.40 1.531 56.0 5 (Second Face of SecondLens) −0.100 0.00 6 (First Face of Cover Glass) 0.000 0.300 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.45 −1.02 3.63E+1 −5.83E+2 3.14E+3 3 2.29E+1 −2.03 3.05E−1−1.17E+2 2.41E+2 4 0.00 −1.48 −1.21E+1 −1.38E+2 2.76E+3 5 0.00 −2.31E−1−2.43 1.04E+1 −3.96E+1

Under such conditions, L/fl=1.12 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.23 was achieved, thereby satisfying theexpression (2). f₁/fl=1.15 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.48 was achieved, thereby satisfying theexpression (4). d₁/fl=0.21 was achieved, thereby satisfying theexpression (5). d₃/fl=0.20 was achieved, thereby satisfying theexpression (6). f₂/fl=4.95 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.62 was achieved, thereby satisfying the expression (9).Bfl=1.255 mm was achieved, thereby satisfying the expression (10).

FIG. 29 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the FOURTEENTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

Fifteenth Example

FIG. 30 shows a FIFTEENTH EXAMPLE of the present invention. In theFIFTEENTH EXAMPLE, like the imaging lens with the structure of FIG. 1, adiaphragm 2 is disposed on the object side of the first face of thefirst lens 3 and a cover glass is disposed between the second face ofthe second lens 4 and the image-taking surface 7, as a filter 6. Thediaphragm 2 is disposed at the same position on the optical axis 8 asthe point on the optical axis 8 on the first face of the first lens 3.

The imaging lens 1 of the FIFTEENTH EXAMPLE was set under the followingcondition.

Lens Data L = 2.40 mm, fl = 2.16 mm, f₁ = 2.44 mm, f₂ = 11.76 mm, d₁ =0.42 mm, d₂ = 0.2 mm, d₃ = 0.4 mm, F no = 4.0 Face Number r d nd νd  (ObjectPoint) 1 (Diaphragm) 0.000 0.00 2 (First Face of First Lens)1.200 0.42 1.531 56.0 3 (Second Face of First Lens) 0.520 0.20 4 (FirstFace of Second Lens) −0.005 0.40 1.531 56.0 5 (Second Face of SecondLens) −0.165 0.30 6 (First Face of Cover Glass) 0.000 0.30 1.516 64.0 7(Second Face of Cover Glass) 0.000   (Image Surface) Face Number k A B CD 2 −1.42E−1 −8.30E−1 1.65E+1 −2.33E+2 1.00E+3 3   1.87E+1 −1.91 −3.22−7.96E+1 6.24E+1 4 0.00 −2.04   7.05 −4.34E+2 4.71E+3 5 0.00 −4.30E−14.66E+1 −8.18 1.24E+1

Under such conditions, L/fl=1.11 was achieved, thereby satisfying theexpression (1). f₁/f₂=0.21 was achieved, thereby satisfying theexpression (2). f₁/fl=1.13 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.48 was achieved, thereby satisfying theexpression (4). d₁/fl=0.19 was achieved, thereby satisfying theexpression (5). d₃/fl=0.19 was achieved, thereby satisfying theexpression (6). f₂/fl=5.44 was achieved, thereby satisfying theexpression (7). S=0 mm was achieved, thereby satisfying the expression(8). Bfl/fl=0.64 was achieved, thereby satisfying the expression (9).Bfl=1.375 mm was achieved, thereby satisfying the expression (10).

FIG. 31 shows the spherical aberration, astigmatism, and distortion ofthe imaging lens 1 of the FIFTEENTH EXAMPLE.

According to the result, each of the spherical aberration, astigmatism,and distortion was almost satisfied. It can be seen from the result thata sufficient optical property can be obtained.

The present invention is not limited to the above-described embodimentsand EXAMPLES, and various modifications are possible as required.

For example, a light amount limiting board can be disposed between thesecond face of the first lens 3 and the first face of the second lens 4as required.

1. An imaging lens used for forming an image of an object on animage-taking surface of a solid image pickup device, comprising: inorder from an object side towards an image surface side, a diaphragm, afirst lens which is a meniscus lens having a positive power whose convexsurface faces said object side, and a second lens which is a lens havinga positive power whose convex surface faces said image surface side,wherein conditions expressed by each of following expressions (1)-(6)are to be satisfied;1.25≧L/fl≧0.8  (1)1≧f ₁ /f ₂≧0.2  (2)1.8≧f ₁ /fl≧1  (3)0.5>d ₂ /d ₁≧0.2  (4)0.35≧d ₁ /fl≧0.1  (5)0.27≧d ₃ /fl≧0.1  (6) where, L: entire length of said imaging lens fl:focal distance of entire imaging lens f₁: focal distance of said firstlens f₂: focal distance of said second lens d₁: center thickness of saidfirst lens d₂: space between said first lens and said second lens on anoptical axis d₃: center thickness of said second lens.
 2. The imaginglens according to claim 1, wherein, said second lens is a meniscus lens.3. The imaging lens according to claim 1, wherein an object side surfaceof said second lens is convex towards said object side in the vicinityof said optical axis and is formed into an aspheric surface having aninflection point.
 4. The imaging lens according to claim 3, wherein anouter end section of an effective diameter of said object side face ofsaid second lens is positioned closer to said object side than a pointon said optical axis on said object side face of said second lens. 5.The imaging lens according to any one of claims 1 to 4, wherein acondition expressed by a following expression (7) is to be satisfied;10≧f ₂ /fl≧1.5  (7).
 6. The imaging lens according to claim 5, whereinsaid diaphragm satisfies a condition expressed by a following expression(8);0.2≧S  (8) where, S: distance between said diaphragm and said opticalsurface closest to said object side on said optical axis.
 7. The imaginglens according to claim 6, wherein a condition expressed by a followingexpression (9) is to be satisfied;0.8≧Bfl/fl≧0.4  (9) where, Bfl: back focus distance (distance from alast lens surface to said image-taking surface on said optical axis). 8.The imaging lens according to claim 7, wherein a condition expressed bya following expression (10) is to be satisfied;2.5≧Bfl≧0.8  (10).